Amorphous calcium phosphate (ACP) has excellent biocompatibility

osteoconduction and biodegradability.However

as it can be transformed easily to a more thermal stable phase

i.e.HAP

ACP shows poor stability in solution.As a soluble and biocompatible additive

regenerated silk fibroin (RSF) can mediate the growth of inorganic crystals.If the RSF is capable of inducing and stabilizing of the ACP

it will be desirable to expand its application to the field of bone repair.The pH value of the mineralization solution increased slowly when the ammonia gas diffused into the solution

leading to the precipitation of calcium phosphate.The morphology and polymorph of calcium phosphates were characterized by SEM

TEM

SAED

XRD and FTIR.Generally

the spherical particles were ACP and the aggregated sheets were HAP in our work.The results also showed that ACP could be obtained by adjusting the mineralization time

the weight concentration of RSF

the molar concentrations of calcium ion and phosphate ion.When the RSF and Ca2+/PO43- concentrations were fixed to 0.5% and 2 mmol/L

respectively

only ACP could be obtained after 1 h; however

both ACP and HAP could be produced when the duration of mineralization was increased to 3 h.Moreover

all the ACP would be transformed to HAP when the time was increased to 24 h.On the other side

when the Ca2+/PO43- concentrations increased

a higher RSF concentration would be needed to induce the growth of ACP.For example

ACP could be produced under a certain condition that the mineralization time and the RSF concentration were 1 h and 1% respectively

supplemental with 3 mmol/L Ca2+/PO43- concentrations

but ACP couldnt be obtained at any concentration of RSF when the ion concentration was reached to 5 mmol/L.Furthermore

it was found that RSF with higher molecular weight could induce the growth of ACP in a lower concentration under the same condition.The stable ACP/RSF hybrid may have the great potential in the bone repairing.